The present invention relates generally to a structure and method for eliminating metal contacts to P-well or N-well shorts when using metal studs, and more particularly eliminates metal contacts to P-well shorts when using metal contact studs by using an N+ doped polysilicon liner, wherein an outdiffusion of N+ dopant from the polysilicon forms an N+ halo extension in the active area silicon, providing a reverse biased junction between the metal contact stud and the P-well. The present invention also relates to the complementary structure and method of eliminating bitline diffusion to N-well shorts when using metal contact studs.
Accordingly, it is a primary object of the present invention to provide a structure and method for eliminating metal contacts to P-well or N-well shorts when using metal studs.
The present invention prevents a short from a metal stud to a P-well which can occur when a contact mask is misaligned with an active area (AA) mask, in combination with an overetch into the isolation oxide of an isolation trench which forms a divot in the isolation oxide, exposing the bitline junction depletion region or even a P-well on the active area mask sidewall to the metal stud. The present invention prevents this problem by using N+ doped polysilicon studs, wherein an outdiffusion of N+ dopant from the stud forms an N+ halo extension in the silicon, providing a reverse biased junction between the stud and the P-well. The present invention also relates to the complementary structure and method of eliminating metal contacts to N-well shorts when using metal studs.
In accordance with the teachings herein, the present invention provides the following advantages over the currently practiced, prior art technology:
it eliminates metal contacts to P-well or N-well shorts when using metal contact studs in a semiconductor device such as an embedded-DRAM or regular DRAM;
it provides contacts in a support which are self aligned to M0 metallurgy. This enables smaller support contacts and denser layouts;
it requires no additional masks or masking steps.
The present invention also provides a structure and method for eliminating metal contacts to N-well shorts when using metal studs. The present invention prevents a short from a metal stud to an N-well which can occur when a CB (contact bitline) contact mask is misaligned with an active area mask, in combination with an overetch into the isolation oxide of an isolation trench which forms a divot in the isolation oxide, exposing the bitline junction depletion region or even an N-well on the active area mask sidewall to the metal stud. The present invention prevents this problem by using P+ doped polysilicon studs, wherein an outdiffusion of P+ dopant from the stud forms a P+ halo extension in the silicon, providing a reverse biased junction between the stud and the N-well.